Dystroglycan is a widely expressed transmembrane glycoprotein that acts as a high- affinity receptor for both extracellular matrix proteins containing laminin-G domains and certain arenaviruses. Secondary dystroglycanopathies encompass a collection of muscular dystrophies characterized by impaired post-translational processing of dystroglycan. Profound muscle weakness and wasting as well as potential central nervous system impariment are typical pathologies associated with secondary dystroglycanopathies. Causative mutations for these disorders are found in known or putative glycosyltransferases that participate in the O-glycosylation of alpha- dystroglycan, a modificaiton required for functionality. Despite extensive efforts to understand the genetics and pathology of these diseases, the genetic causes of over half of these cases remain a mystery. Furthermore, there are no treatments available for patients. This proposal outlines approaches to elucidate remaining genetic causes of dystroglycanopathies, discover and validate small molecule and peptide effectors of dystroglycan glycosylation and provide the muscular dystrophy field with improved mouse models to sustain rapid future progress. These goals will be successfully met through collaboration with the Schultz laboratory at The Scripps Research Institute. The objective of Specific Aim 1 is to identify novel dystroglycanophy genetic loci using both high-throughput in vitro complementation and knockdown screens. Elucidation of new candidate genes will offer new opportunities for improved genetic diagnosis, new viable therapeutic targets and a better understanding of dystroglycan post-translational processing. Specific Aim 2 is designed to identify novel small molecule and secreted peptide effectors of dystroglycan glycosylation in a cell culture based, high-throughput manner. This unbiased approach will provide new directions for the development of therapeutic interventions for muscular dystrophy. Specific Aim 3 is targeted at both validation of previously and newly identified therapeutic strategies and the development of conditional and knockdown mouse models of dystroglycanopathy. The new mouse models will better capture both the genetic and phenotypic complexity of dystroglycanophies than the currently available cohort of mouse models. These models will serve the muscular dystrophy research community in efforts to explain the cellular mechanism and to develop viable treatment strategies for each genetic cause of dystroglycanopathy. These studies will provide the muscular dystrophy research field with improved tools and progress towards suitable means of improving dystroglycan function. This research meets the challenge of the National Institute of Neurological Disorders and Stroke mission statement to support "research on the causes, prevention, diagnosis, and treatment of neurological disorders and stroke, and supports basic research in related scientific areas". PUBLIC HEALTH RELEVANCE: Muscular dystrophies are a diverse set of inherited diseases characterized by progressive skeletal muscle weakness and wasting. Dystroglycan, a cell surface protein, requires extensive modification to serve as a link between the intracellular and extracellular cellular support network in muscle such that, when disrupted, it results in several forms of muscular dystrophy. This proposal is designed to identify new gene mutations that can cause these types of muscular dystrophy, discover small molecules that can improve dystroglycan function, develop needed mouse models of the disease and to validate both newly identified and currently known treatment strategies.